The present invention relates to installations for electroslag melting of heavy-weight metal ingots.
Commonly known are installations for electroslag melting of metal ingots, having vertical columns which mount at least one electrode holder to fix therein one or several consumable electrodes and to feed electric current to them. Mounted on the columns below the electrode holder with possible vertical displacement is a cooled mould positioned on a cooled bottom plate forming a bottom of the mould.
The mould has a through cavity whose upper portion has a wider cross section than the lower portion.
The wider upper portion of the cavity of the cooled mould is intended to accommodate a slag bath and to melt consumable electrodes therein, while the lower more narrow portion of the cavity of the cooled mould is intended to collect molten metal for its crystallization into an ingot. The value of the cross section of the lower portion of the cavity is selected so as to be substantially close to the value of the cross section of the consumable electrode subject to melting or to the total value of the cross-sectional areas of several consumable electrodes subject to simultaneous melting-down.
In the course of electroslag melting of metal, the consumable electrodes and the bottom plate remain stationary, while the cooled mould is moved upward as the ingot is being built up.
In an installation described in U.S. Pat. No. 3,713,476, a hollow cooled mould is placed on a bottom plate having a protrusion which at the beginning of melting completely enters the cavity of the mould from underneath. The upper end face of the protrusion is positioned considerably below the ingot forming section of the cooled mould.
A space is left above the protrusion in the lower portion of the cooled mould cavity for forming the bottom portion of the metal ingot being produced. In the course of melting the ignot, first portions of melted metal solidify the end face of the protrusion.
With the height of a built-up metal ingot increasing, the cooled mould is raised correspondingly.
The rate of ingot growth and correspondingly the rate of raising the cooled mould are selected with respect to conditions ensuring the melting of a high-quality metal ingot. For this purpose the cooled mould is moved upward so that almost the entire upper portion of a crystallized ingot is located in the lower ingot-forming section of the cooled mould.
On completion of melting the consumable electrodes, the cooled mould is emptied of slag. Also removed are discarded ends of the consumable electrodes together with standard parts of electrodes, to which the ends of consumable electrodes are attached (welded). The cooled mould is moved upward until a produced metal ingot fully goes out from its lower portion, thereafter a carriage with the bottom plate together with an ingot placed thereon is rolled out of the melting installation.
Usually used with this known installation for melting metal ingots weighing from 150 to 200 t and heavier are relatively short consumable electrodes, with the length of each of them equal to the height of an ingot being produced. The consumable electrodes are secured in an electrode holder mounted on a relatively simple metal structure, for example, columns with guide members for vertical displacement of the cooled mould longitudinally in relation to the columns.
So, the known installation is able to solve the problem of producing heavy-weight metal ingots.
However, the known installation cannot do without relatively long standard parts to which consumable electrodes are welded. In melting ingots weighing up to 200 t, the length of the standard parts is as much as 4 to 5 m. This is dictated by the fact that on completion of the melting process the cooled mould should be raised until the head portion of an ingot goes out of the cooled mould cavity. And because the consumable electrodes are secured stationary on the standard parts the reserve upward stroke of the cooled mould along the columns can be ensured only as a result of increasing the length of the standard parts at least by the value of the height of the ingot forming wall portion of the mould. This height for ingots weighing 200 t is from 1.5 to 2.0 m.
The increased length of the standard parts of the electrode holder leads to growing resistance and inductive reactance of the furnace and this in turn results in a more powerful source of electric energy needed for feeding the installation.
Due to the use of long standard parts the known installation is of a relatively large height and this consequently requires more materials, usually steel, to be needed for its manufacture.